Neurobehavioral and Neuroendocrine Assessment of Rats Perinatally
Total Page：16
File Type：pdf, Size：1020Kb
NEUROBEHAVIORAL AND NEUROENDOCRINE ASSESSMENT OF RATS PERINATALLY EXPOSED TO POLYCHLORINATED BIPHENYLS: A POSSIBLE MODEL FOR AUTISM Dena N. Krishnan A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2007 Committee: Lee A. Meserve, Advisor Howard Casey Cromwell Mike Geusz Luke Tsai ii ABSTRACT Lee A. Meserve, Advisor Several studies have shown that perinatal exposure to xenobiotic mixtures such as polychlorinated biphenyls (PCBs) can cause physiological and behavioral disruption. These studies demonstrate that PCB-exposed rats are a possible model for understanding motor and social deficits in childhood developmental disorders like autism spectrum disorder (ASD). The mixture PCB 47/77 at 0 ppm, 12.5 ppm, or 25 ppm (w/w) of the diet was fed to pregnant Sprague-Dawley rats impacting offspring both indirectly and directly from GD 1 to PND 21. Motor functioning of offspring was tested at PND 14-16, 28-32, and 60-64 with measures of general motor activity and stereotypic repetitive behavior. Subsequently, t-maze learning acquisition and reversal was tested in males 25-29 days old and circulating levels of the hormone vasopressin were measured at 29 days of age by enzyme immunoassay. Numerous motoric impairments were found in PCB-exposed rats compared to controls including: 1) altered rates of activity, 2) significant delay in the formation of grooming chain syntax, 3) a longer latency in pup righting reflex, and 4) depressed ability to complete the hang and negative geotaxis tests at various stages of development. PCB-exposed rats showed a significant delay in t-maze learning aquisition and reversal in a dose dependent manner relative to controls. These consequences likely stem from neuroendocrine disruption despite no change in systemic circulating vasopressin concentration. The different results in animals given 12.5 ppm and 25 ppm PCB suggest use of this animal model to reveal a range of motoric disruption similar to the broad autistic phenotype. iii DEDICATION To all the challenges and disappointments that make success worth striving for. iv ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Dr. Lee Meserve, for helping me grow as a graduate student, teacher, and researcher. It is by his example, support, encouragement, and sense of humor that I have developed a true passion for neuroendocrine research. I thank my other committee members: Dr. Howard Casey Cromwell for inspiring my behavioral work, Dr. Mike Geusz for his insightful suggestions, and Dr. Luke Tsai for his advice in making appropriate clinical connections. I would like to acknowledge my fellow lab associates, Banafsheh Jolous- Jamshidi, Avanti Desai, and Christina Asbrock for their companionship; and to the many undergraduate scholars, especially Trang Tran and Travis Beckwith for their meticulous involvement with the collection and scoring of my behavioral data. I wish to thank Matt Hoostal because without his coaching and expertise, I would still be grappling with my statistics. I extend my sincerest gratitude to the faculty, staff, and graduate students of the Department of Biological Sciences for making my time at Bowling Green State University so enjoyable. In particular, I must thank Lorraine DeVenney for making me an offer I could not refuse and will never forget. Lastly, I acknowledge my parents, family, and friends near and far for their love and support. I especially want to thank my brothers: Josh for teaching me more about neuroscience than I ever wanted and Anoop for being my number one fan. Thank you all for enriching my life and helping me achieve this important goal. v TABLE OF CONTENTS INTRODUCTION………………………………………………….....…………………1 MATERIAL AND METHODS……………………………………………………...….15 RESULTS NEUROBEHAVIORAL ASSESSMENT: Developmental Motor Activity: Open Field………………………………………………………..24 Hang Test…………...……………………………………………26 Negative Geotaxis Response……………………………………..27 Righting Reflex…….……………….……………………………29 Stereotypic Repetitive Behavior: Grooming………………………………………………………...30 T-maze Acquisition and Reversal…………………………….….34 Summary of Behavioral Results………………………………………....37 NEUROENDOCRINE STATUS: Circulating Vasopressin Concentrations………………………………....38 DISCUSSION………………………………………..…………………………………..39 REFERENCES……………….……………………………………………...…………..52 APPENDICES……………………………………………………………………...……61 vi LIST OF FIGURES Figure Page 1. Conceptual Idea of Term “Autism Spectrum Disorder” (ASD)……..….…….1 2. Structure of Polychlorinated Biphenyl (PCB) Molecule………..….…………5 3. The Neurohypophysis……………………………….……………...………..11 4. Choreographed “Syntactic Chain” Sequence of Grooming Actions………...19 5. Effect of PCB on Mean Horizontal Movement during Development……….24 6. Effect of PCB on Mean Rearing during Development………………………25 7. Effect of PCB on Development Mean Rear Time.……………………….….25 8. Effect of PCB on Development Mean Hang Test…………………..….…….27 9. Effect of PCB on Developmental Mean Negative Geotaxis Response……...28 10. Effect of PCB on Developmental Mean Righting Reflex.. ………….………29 11. Mean Total Grooming/ Rat ………………………………………………….31 12. Mean Chains Initiated/ Rat…………………………………………………..31 13. Percent Complete Perfect Chains ……………………………………………32 14. Percent Incomplete Chains…………………………………………………..32 15. Percent Complete Imperfect Chains…………………………………………33 16. Effect of PCB on Mean T-maze Acquisition in Juvenile male rats………….34 17. Effect of PCB on Mean T-maze Reversal Learning in Juvenile male rats…..36 18. Effect of PCB 47/77 on Mean Circulating Serum Vasopressin Concentrations in 29-Day Old Male Rats. ……………………………………………………….38 vii LIST OF TABLES Table No. Page 1. Timeline for first set of litters tested…………………………………….…...16 2. Timeline for second set of litters tested……………………………….……..16 3. Sample Size for all Open Field Parameters Tested…………………………..26 4. Sample Size for Mean Hang Score…………………………………………..27 5. Sample Size for Mean Negative Geotaxis Response………………………...28 6. Sample Size for Mean Righting Reflex……………………………………...29 7. Sample Size for all Grooming Parameters Tested…………………………...33 8. Sample Size for Mean Learning Days……………………………………….34 9. % Rats Meeting Acquisition Criteria ………………………………………..35 10. Sample Size for T-maze Reversal……………………………………………36 11. Summary of Behavioral Results in Rats Exposed to PCB 47/77 at 0, 12.5 and 25 ppm ……………………………………………………....37 12. Sample Size for Serum Vasopressin Analysis……………………………….38 13. Comparison of PCB Congeners/ Doses and Motor Outcomes……..………..40 14. PCB Exposure as a Possible Animal Model for ASD……………….………51 1 INTRODUCTION Autism spectrum disorder (ASD) is a term used to describe a group of developmental disorders associated with substantial deficits in three specific areas: (1) reciprocal social interaction, (2) communication, and (3) the presence of repetitive and stereotyped behaviors and unusual interests (DSM-IV; American Psychiatric Association, 1994). These core clinical features generally appear before age 3 and last throughout a lifetime. ASD occurs in all racial, ethnic, and socioeconomic groups and is four times more likely to occur in boys than girls (CDC, 2007; Tsai 1999). The definition of ASD has evolved since Kanner first described the disorder in 1943 (Kanner, 1943), and now encompasses a wide range of behavioral severity with varying levels of cognitive and linguistic functioning (Tsai and Ghaziuddin, 1996). The term ASD includes the commonly recognized disorder autism, as well as Asperger’s syndrome, and pervasive developmental disorders not otherwise specified (PDDNOS). Since the etiology of ASD is unknown, the heterogeneity originally described on a continuum or “spectrum,” is presented here as different syndromes with overlapping clinical features (Figure 1). Autism Asperger’s PDDNOS Figure 1: Conceptual Idea of the term “autism spectrum disorder” (ASD). (Adapted and modified from Tsai, 1999) 2 Across ASD, the social domain may range from a complete absence of interest in interacting with others to more subtle difficulties managing complex social interactions that take into account the intentions of other people (Pelphrey et al., 2004). Individuals with Asperger’s syndrome tend to be argumentative and aggressive with a condescending affect, features rarely seen in individuals with autism (Ghaziuddin et al., 1991). Stereotypic repetitive behaviors may range from abnormal gait and preference for sameness to more complex elaborate rituals (Tsai and Ghaziuddin, 1996). Language deficits, while marked in some autistic individuals who are deemed completely nonverbal, can be mild and limited to the presence of pragmatic language deficits in higher functioning individuals with autism (Hollander, 2003; Koger et al., 2005). Several studies have implicated environmental factors as acting synergistically with genetic factors to cause the broad autistic phenotype (Hollander, 2003). Much of this literature focuses on heavy metals such as mercury and lead and commercial chemicals such as polychlorinated biphenyls (PCB) because of their direct neurotoxic, endocrine disrupting potential (Hubbs-Tait et al., 2005). Young children often encounter higher levels of toxicants than adults due to what Weiss (2000) calls the unique “spatial ecology” of childhood. Young children spend considerably more time on the floor breathing dust, drink breast milk, and ingest more juice, fruit and water, giving them increased exposure to pesticide residues and contaminants than adults (Koger et al., 2005). It is well